This invention relates to circuits exhibiting hysteresis and, in particular, to a circuit capable of producing a well defined and controlled amount of hysteresis.
In circuits exhibiting hysteresis the value of the input signal for which the output signal switches from one state to another depends on whether the input signal is increasing or decreasing. Thus, for example, when the input signal is increasing and reaches a first threshold level, the output switches from a first state (e.g., high) to a second state (e.g., low) and remains in the second state for all values of the input signal in excess of the first threshold level. When the input signal is decreasing, it must reach a second threshold level, different from the first level, to cause the output to switch from the second state to the first state. Such circuits thus exhibit two different threshold levels; one threshold when the input voltage is increasing and the other threshold when the input voltage is decreasing.
Circuits exhibiting hysteresis have increased noise immunity and are therefore extremely useful for reliable operation in an electronically noisy environment. Such circuits are also useful for converting slowly varying signals into pulses having well defined and sharp leading and trailing edges. There is therefore a need in many applications for circuits exhibiting hysteresis and for circuits where the amount of the hysteresis is stable and well defined.